1. Technical Field
The present invention pertains to the field of communications networks, in particular to the field of data transport networks.
2. Description of Related Art
List of Acronyms:
ACTAccess Control TagANIActive Node IdentifierBCRBus Capacity RequestBTSByte TSEOBEnd-Of-BusLNILocal Node IdentifierQoSQuality of ServiceSDHSynchronous Digital Hierarchy, ITU-TRecommendations G.707 and G.783SONETSynchronous Optical Network, a subsetof SDH used in North AmericaTDMTime Division MultiplexingTSTime-Slot
In communications networks, circuit-switching is generally used to provide connections of pre-definable and guaranteeable quality of service (QoS) between communicating nodes such as switches or terminal equipment. The QoS of a connection is typically defined with parameters such as data transmission bit rate, latency, bit error rate, and maximum down-time, which are straightforwardly defined for a pre-provisioned circuit-switched connection, as the bandwidth of such circuit is dedicated for it and can not be consumed by any other traffic in the network. However, for multi-point packet traffic with unpredictable traffic load variations, such as Internet traffic, a network based on pre-provisioned circuits that have constant bandwidth and coarse connection bandwidth granularity is inefficient, as the connection capacities do not adapt according to the packet traffic load variations across the network. For packet-based data traffic, an alternative for circuit-switching is packet-switching, which however requires complicated packet processing, network resource reservation and session initiation protocols in order to provide pre-definable QoS.
Conventionally, high-bandwidth traffic flows, e.g. Internet traffic between a set of Point-Of-Presences (POPs) of an Internet Service Provider, is carried in networks over dedicated point-to-point connections. As the load variations of Internet type of packet traffic over time are unpredictable, it could be that at some given time most or even all the traffic from a given one of the said set of POPs, called POP A, is destined toward a single one, called POP B, of said set of POPs. Therefore, in order to not limit the billable traffic throughput of the inter-POP network, conventionally between said POPs A and B is provisioned a semi-permanent connection of constant bandwidth equal to the traffic forwarding capacity of POP B (or that of POP A, if smaller). In alike manner, using conventional non-dynamic connection based networks, similar pre-provisioned connections, each with constant bit rate equal to the traffic forwarding capacity of the destination POP, would be needed in order to not create blocking within the inter-POP network. At the same time, a given POP can forward traffic only up to its fixed maximum aggregate data rate, and therefore the conventional architecture based on pre-provisioned, non-dynamic point-to-point connections is not optimal for unpredictable, bursty data traffic. Installing additional intermediate packet switching nodes within such inter-POP network can help reducing the total network capacity required for the non-dynamic point-to-point links, but such additional intermediate packet switching points will however deteriorate the traffic QoS by increasing delay, delay variation and packet loss rate, and consequently will lower the effective client traffic throughput i.e. the volume of in-time delivered data packets.
Due to the rapid growth in Internet and other data traffic, and due to importance of pre-definable QoS for a reliable, high-quality communications service, there is a need for a network alternative that is based on and interoperable with standard circuit-switched legacy networks, in particular those based on the widely deployed SDH/SONET protocols, but that provides means for dynamically adapting the bandwidth of the circuit-switched connections across the network based on real-time packet traffic load patterns, in order to optimize the data traffic throughput of a network of given physical capacity.